This invention relates to a speed-change and steering system for crawler type vehicles.
Heretofore, a power transmission system for changing a speed of a crawler type vehicle or steering it has been known. In one of such known speed-change/steering systems for crawler type vehicles, as shown in FIG. 1, a first shaft a coupled to an engine E is connected to first and second pumps c.sub.1 and c.sub.2 via gear means b, first and second motors d.sub.1 and d.sub.2 driven by the pumps c.sub.1 and c.sub.2, respectively, are connected via gear means f to a plurality of planetary gear means e mounted on the first shaft a and planetary gear means n and p mounted on a third shaft m, the first shaft a is connected to the planetary gear means e or a second shaft l by switching ON or OFF a plurality of clutches k mounted on the first shaft a, the planetary gear means e is connected to the second shaft l via gear means q, the second shaft l is connected to the planetary gear means n via gear means g, a first output shaft h is connected to the planetary gear means n, the second shaft l is connected via gear means i to the planetary gear means p, a second output shaft j is connected to the planetary gear means p, the clutches k are switched ON or OFF, and delivery volumes of the pumps c.sub.1 and c.sub.2 are changed, this a crawler type vehicle is changed in speed or steered in either direction (For example, refer to Japanese Patent Application Laid-open Specification No. 55-091418).
With the above-described power transmission systems, althrough it is possible to smoothly change the speed of or to steer a crawler type vehicle, on the other hand, since the first shaft a, second and third shafts l and m and the first and second pumps and motors c.sub.1, d.sub.1, c.sub.2 and d.sub.2 are disposed in juxtaposition, the overall system becomes very large-sized, and further since a large power is transmitted also to the second and third shafts l and m, the second and third shafts must be supported so as to bear against the heavy load, and therefore, this system has a disadvantage that the number of component parts becomes large and the weight of the system becomes heavy.